Electric contact plug



D. E. WADSWORTH 2,229,151

ELECTRIC colmkct PLUG Filed lamb 11, 1938 5 shoeta sheot 1 vn a Jan. 21, 1941.

' INVENTOR DUMLD E WADSMH QEHHEEIILW .4

ATTORNEYS Jan. 21, 1941. 5 WADSWORTH 2,229,151

ELECTRIC GOMAGT PLUG I Filed larch 11, 1936 5 Shoots-Shoot s FIG. 5.

P-fl 15 INVENTCR DONALD E. WAOSWORTH BY I ATTORN EY I JUL D. E. WADSWORTH' I 2,229,151 I ELECTRIC CONTACT PLUG Filed larch 11 1936 s sums-shut 4 INVENTOR DONALD E. WAOSWU/FT H 1941- O D. E. WADSWORTH 5 ELECTRIC CONTACT PLUG 'Filed March 11, 1936 5 Shoots-Shoot 5 INVENTOR ATTORNEY$ 00mm amoswo/m/ g with a screw socket, for instance, and in otherv Patented Jan. 21, 1941 UNITED STATES PATENT OFFICE 2,229,151 suzc'riuc course's PLUG Donald 11L Wadsworth, Bloomfield, N. J. Application March 11, ms, Serial No. 195,286

15 Claims. (01. 173-381) This invention relates to electrical contact plugs and more particularly to a dual P p se plug adapted to be used as a screw-in plug wherein electrical connection is adapted to be made situations'wherein electrical contact is adapted to be made by contact prongs.

It has heretofore been proposed to provide a dual purpose contact plug having a threaded conductive shell for reception in the lamp socket and a contact centrally thereof for electrical connection with a center contact or 'the lamp socket, while at the same time having a pair of contact prongs adapted to enter and make electrical connection with the electrical contacts of electrical connectors such as outletfittings. In the dual purpose contact plug heretofore known, a member carrying the threaded conductive shell was reciprocable into and out of operative position but the center contact and the threaded shell were at all times in electrical connection with the contact prongs, thereby affording a plurality of electrical contacts with the likelihood that certain of the contacts would be exposed and create the danger of short circuit or electrical shock to the user. Moreover such-prior dual purpose contact plug made no provision for retaining the parts in either operative position so that the device was, to all intents and purposes, diflicult to handle and manipulate.

One object of the present invention is a dual purpose plug of the character described having means to retain the respective'parts in either position of adjustment.

Another object of the invention is a dual purpose contact plug in which the contacts not in use are not in the electrical circuit or are otherwise protected or insulated.

It is also an object of the present invention to provide a dual purpose contact plug wherein the parts are retained against displacement in either selected condition of use.

The invention also seeks a dual purpose contact plug which is practical from the standpoint of ease and cheapness of manufacture and durability and safety in use.

In one of its aspects, the invention has to do with a dual purpose contact plug comprising a cup-shaped body member having spaced contact prongs carried therewithin and extending therewithout and upon which a threaded shell carrying member is reciprocable into and out of the bodymember, said threaded shellcarrying member being formed with an axial bore into and out of which a central contact member is adapted to reciprocate. I

In accordance with. another aspect of the in- .vention, the dual purpose contact plug comprises These and other objects of the invention and the means for their attainment will be more apparent from the following detailed description, taken in connection with the accompanying drawings illustrating one embodiment by which the invention may be realized, and in which:

Figure 1 is a view, in longitudinal section,

showing the dual purpose plug of this invention with the parts disposed ,for reception in a lamp socket; g

Figure 2 is a fragmentary, longitudinal, sectional view taken in the same plane as Figure 1 but showing the central contact member with its parts in partially retracted position in the threaded reciprocable plug member portion preparatory to these parts being withdrawn into the cup shaped body portion;

Figure 3 is a longitudinal, sectional view of the dual purpose plug taken in the same plane as that of Figure .1 but with the parts in fully retracted position;

Figure 4 is a fragmentary, sectional view taken in the plane indicated by the line 44 of Figure 1 and looking in the direction of the arrows and showing the instrumentalities by which separation of the body and threaded plug is prevented when the parts are in protracted position;

Figure 5 is a view showing the dual purpose plug of this invention with the parts in the same position as that in Figure 1, but taken in a longitudinal plane perpendicular to the plane of Figure 1 and in the line 5-5 of that figure,-

and looking in the direction of the arrows;

Figure 6 is a transverse, sectional view of the central contact carrying member, taken in the plane indicated by the line 6--6 of Figure 5 and looking in the direction of the arrows;

Figure 7 is a longitudinal, sectional view of the dual purpose plug of this invention with the parts in the same relative position as that shown in Figure 3 but taken in a plane perpendicularthereto along the line 'I'l of Figure 3 and looking in the direction of the arrows;

Figure 8 is a fragmentary, transverse, sectional view showing the bottom of the cup shaped body member of this invention, taken in the plane indicated by the line 8-8 of Figure 1 and looking in the direction of the arrows;

Figure 9 is a top plan view looking down on the dual purpose plug of this invention with the parts in the position of Figures 3 and '7 and taken in the plane indicated by the line 9'9 of Figure 3, looking in the direction of the arrows, the contact prongs being in section;

Figure. 10 is a side elevational view of the central contact carrying member as viewed in the plane indicated by the line Ill-l in Figure 1 and looking in the direction of the arrows;

and

Figure 11 is a view showing the central contact member in elevation looking from the right as viewed in Figure 10, on'the line of that figure.

The dual purpose contact plug of this invention comprises generally a cup-shaped body member I of non-conductive material, such as a mouldable material, within which is mounted a pair of contact prongs ll, I9, extending longitudinally thereof and protruding a sufficient distance to permit them to be entered into and make electrical connection with the electrical contacts of electrical connectors, such as outlet fittings. .Reciprocable into and out of the cupshaped body member I5 is an insulatory member 2| carrying a threaded conductive shell 23 for reception in a lamp socket or the equivalent, and herein called the threaded shell member, and a contact carrying member 25 centrally thereof for electrical connection with a center contact of a.

lamp socket, the invention being generally so conceived and proportioned that when the dual purpose plug is to be used in connection with a lamp socket or the like, the contact prongs ll, l9 are concealed from view and insulated against all outside contact, while the threaded shell 23 and the central contact 21 are live, they being in electrical connection with the electrical con ductors to which the plug is attached. On the other hand, when this threaded shell 23 and central contact 21 are retracted into the body of the body l5, the threaded shell 23 and central contact 21 are rendered inoperative so that no electrical current is carried by them.

The lower end of the body member I5 is provided with a removable closure or cap 29 which conceals and protects the connections 3| with flexible electrical connectors.

Referring first to Figures 1 and 5, the dual purpose plug of this invention comprises preferably a one-piece body l5 formed with a preferably but not necessarily cylindrical bore 33 defined by the cylindrical wall. 35 and an integral bottom 31.

.In its lowermost portion is a part 39 of reduced diameter which is conveniently threaded for the removable reception of a generally cup-shaped end member or cap 29 adapted to conceal the contact screws 3| by which electrical conductors, not shown, are secured in electrical connection with the conductive parts of the plug and formed with an aperture 4| preferably centrally thereof through which the conductors may pass. As shown, the bottom of the cup-shaped member 35 is conveniently formed with spaced recesses or grooves 43, conveniently diametrically opposite one another, in which the ends of the conductors, not shown, lie. The ends of the conductors may be further separated and insulated from one another by the downwardly projecting boss 45.

Mounted in the bottom 31, as by moulding or other convenient manner of securement, are the two spaced contact prongs I1, I9, of usual conformation, generally speaking. At their lower ends, these contact prongs I9 are each provided with a generally outwardly and somewhat downwardly extending end portion 41 lying with- I in the aforesaid depressions or grooves 43 and tapped for reception of the contact screws 3| by which the ends of the electrical conductors are secured to the contact prongs for electrical connection therewith. Proximate these oilset ends, ears 49 are, conveniently struck out from the prongs I], I9 to lie in transverse planes thereof for reception in recesses 5| in the bottom 3'! of the body, it being understood that these are conveniently secured in position in any convenient manner, as by moulding them therein during the formation of the cup-shaped body. The bottom 31 of the cup-shaped body |5is also conveniently formed with recesses 53, one proximate the outer or remote surface of each prong l1, IQ for a purpose which will hereinafter be described and with generally longitudinally extending bores 55 for the reception of the respective threaded ends 51 of the securing screws 3| during their reciprocation. outwardly of the mouth of the body member IS a distance sufficient to function in making the usual electrical connection with the electrical contacts of electrical connectors such as outlet fittings. Intermediate the inner and outer ends of the contact prongs, ears 63 are struck outwardly therefrom, as shown, to serve conveniently as stop members for preventing the separation of the shell member 2| from the body member l5 when the parts are in extended position. At some convenient point between the bottom of the concave body member and the positioning ears 63 aforesaid, the prongs l1, l9 are shown as recessed or grooved as at 65, serving as one of a pair of latching instrumentalitles retaining the parts in retracted position, as will be explained hereinafter more fully.

The threaded member 2| is also conveniently formed as a body 61 of non-conductive material,

such as a moulded or mouldable composition. It is generally cylindrical and of such axial length as to abut against the flat bottom surface of the cup-shaped body member and lie wholly below the rim of the cylindrical wall 35 thereof, when in retracted position. Conveniently secured to the outer periphery of this non-conductive plug member, is the threaded cylindrical shell 23 for reception in a lamp socket or the like. As shown, at its lower portion, the plug member 61 is of slightly increased diameter, as at 69, and the shell member is grooved or otherwise formed with one or more indented portions H (Figure 5) to prevent axial and/or circumferential displacement of the shell with respect to the plug body. The lower surface 13 of the threaded plug member 61 is flat, as shown, to seat on the generally flat bottom surface 15 of the cup interior. The upper or outer end of the threaded plug member 61 is concave as at 16, or dish-shaped and the upper rim 11 of the threaded shell 23 is bent over and conveniently seated in or moulded within the concave surface so that the outer top surface of the shell is continuous with the end surface of the plug member.

The thread carrying plug member 61 is formed with an axial bore 19, conveniently, but not necessarily, of rectangular cross section and one pairof opposed walls 80, 80 of this bore is longitudinally grooved, preferably with a groove 8|,

Conveniently the prong members extend tact plate at one perpendicular to the plane of the aforementioned grooves 8 I, 83, the wall of the bore is formed with a longitudinally extending groove 81 opening at its lower end in the lower surface of the reciprocable plug member, but extending upwardly toward the other or concave upper end a distance short of the concave surface so that material of the plug forms a shoulder or stop 89, Figure 5, for the central contact carrying member 25.

In the central rectangular bore of the reciprocable plug member, reciprocates a central contact carrying member 25 illustrated in front and side elevation in Figures 10 and 11 and in top plan in Figure 9. This'member rests within the rectangular'bore with sufllcient clearance for freedom of movement. Its upper surface 88 is convex. It is conveniently formed of non-conductive material. At its upper end, on diametrically opposite sides, it is conveniently formed with recesses 9I of V-shaped longitudinal crosssection so that the ends 93 of a metallic plate 21 overlying and preferably embedded in-at least the central portion of the convex top, as viewed in Figure 7, may be bent downwardly and under the downwardly inclined walls 91 of the recesses 9| to firmly position the metallic plate in position. This plate serves as the central contact.

Conveniently the respective lower surfaces 99 of the recess are formed on a curve merging with the curve of the concave upper surface 18 of the tion of the contact carrying member.

the web I85 and extending in planes transverse plug member 2| so as to facilitate engagement with, say, the thumb and finger thereby to grasp the contact carrying member and withdraw it from the threaded reciprocable plug from the retracted position shown in Figure '7 to the protracted position shown in Figure 5.

In a plane transverse to the plane of the recesses or finger grips 9|, the lower portion of one pair of sides of the contact member 25 is formed with recesses IN. The bottom of each recess is defined by a transverse web portion I85 while Y the upper end of each recess is conveniently formed on the arc of a circle. The inner proximate surfaces of the recesses I8I become progressively deeper from the upper curved end toward the lower flat bottom end so that the longitudinal surfaces for an appreciable distance are inclined, as at I81, and then, for convenience in manufacture, the surfaces are parallel to one another, as at I89, down to the transverse web I85 which serves as the bottom of the central por- Beneath to the plane of the recesses I M and along the side edges of the central contact carrying member are downwardly depending flanges or side walls I32 defining a transverse recess-or groove for a leaf spring member I28, lil hereinafter to be described. In the recesses I8I are pivotally carried insulatory stop members III which have side thereof and with the contact plate is moulded into the material of the member so that it enters the slot at the curved upper end thereof inwardly of a side wall. The lower end of this conductive strip I I3 is angularly bent in an inward direction as at H5 and again beint downwardly, as at I", to form a shoulder or latching recess which, as viewed in Figure 1, is adapted to engage the end of one contact prong, say, II, to form electrical connection therewith and retain the contact member 25in extended position. The free portion II9 of this contact strip is embedded in the insulatory body III which is formed, at the upper end thereof, with a recess whereby some freedom of movement is permitted of the contact strip. The shape of thismember II I is such as to afford insulation and reinforcement to the strip throughout substantially its entire length except at the shoulder which is e posed and the normal position of the same is such that the contact strip has an inherent tendency to spring outwardly against the surface of the body is retracted into the plug, as shown in Figure 3, but this semi-cylindrical portion I2I is of such form or shape as to be .received in the groove or recess 65 in the respective contact prongs I'I, I9, as shown in Figure 3, to function as a spring pressed latch retaining the reciprocable threaded plug in the retracted position of Figure 3.

Diametrically opposite III) a similar contact strip I23, which as before, is moulded within the interior of a body III, as shown, and forms a second contact member for engagement with the end of the other contact prong. Here again the shape and function of the device and its reinforcing and insulatory enclosing body is the same as that described and like reference characters are used throughout. Joined with this contact strip I23, within the body of the contact carrying member 25, is the upper end I25 of a leaf spring also formed therewithin during the process of manufacture, as shown in Figure 5, which exthe contact prong II. At the lowermost portion tends downwardly within the body and then outwardly around 'a boss I21 moulded integral with the body, as shown, and then inwardly as at I28 to be movable in the open ended transverse groove I29 formed in the bottom end of the member 25. This spring member is then reversely bent, as at I3I, beneath the bottom Ofthfi member and when compressed (Figure 7) the parts I28, I3I lie within the transverse groove I29 which is shown as formed by the two depending walls I32 beneath. the web I85 there shown. The bottom portion I33 of this spring member extends downwardly and outwardly and is received within a slot I35 formed in the wall of the reciprocable threaded shell carrying member 61 with itsend portion I 91 in electrical connection with the conductive shell 23.

It will be observed from an inspection of Figures 1 and 5' that the electrical connection may be made from the central contact 21 to the contact prong through the leaf spring H9 on' the 1 shaped in manufacture as to normally assume the position shown in Figure 7, with the arms tension and so soon as the two latching members I I I are drawn together into the opposed slots I0 I,

so that they are free, inwardly, of the ends of the prongs, the leaf spring has a tendency to draw this central member downwardly to its innermost position as shown in Figure 3 andretain it in that position.

To prevent separation of the parts, that is the body I5 and shell member 2I, companion stop membersare carried with the shell member 2I. These are shown as U-shaped members, seen in side elevation in Figure 4. The arms I II of the U are spaced a distance suflicient to receive therebetween the struck out lugs 63 on the prongs I'I, I9. The upper ends of the arms I II are bent outwardly and downwardly as shown at I43 for reception in recesses I45 in the side walls of the longitudinal grooves 8| and 83. These arms have some degree of inherent resiliency so .that they may be easily inserted and snapped into place in the recesses I45 during assembly, if desired. Y

The operation of the device will be apparent from the foregoing description. Assuming" the parts of the dual purpose plug in the position of Figures 3 and 7, the parts will be retained in that position by reason of the fact that the central contact carrying member is retained in fixed retracted position within the body by virtue of the entrance of the latching lugs I2I within the recesses 65 in the prongs. Relative movement between the threaded shell carrying member 2| and the central contact carrying member 25 is prevented at this time by the latching means I2I,

65. It will also be apparent that, irrespective of the latching means I2I, 65, the contractile tendency of spring I28, I3I tends to draw the central contact member 25 downwardly into the bore of the member 2I and tends to hold it there. The spring I28, I3I .may also be utilized as a limiting stop for the member 25 in its lowermost position. Thus, that portion I34 of the spring leaf I28 under the boss I21 abuts, under the influence of the spring, the portion I31 of the spring leaf I3I. At this time, the central contact member is not in electrical connection with the prongs so that in no circumstances can the central contact cause a short circuit or ofier an exposed surface which might give rise to shock to the user or a spark to some other conductive part. Again the threaded shell 23 is similarly out of electrical connection with the contact making screws 3| by reason of the fact that the conductive spring I28-I3I is out of electrical connection with the contact prong by reason of the fact that the leaf spring contact member I23 is retained in spaced position from the prong and is insulated therefrom. Further the material of the central contact carrying member insulates the two leaf spring contacts H9 and I23 from one another and when these contacts are within the recesses of the member, they are completely insulated and all contact with outside conductive surfaces is prevented.

To change the relation of parts and render the shell carrying member operative, it is merely necessary to reach within the prongs with the thumb and forefinger and grasp the member 25 by the opposed recesses 9|. Withdrawal of the member 25 brings with it the shell carrying member 2|. That member is stopped in opera tive position by the interconnection of the stops 83 and Ill.

The central contact member may be further moved to extended or final stop position when stops 89 and I2! engage, this being permit ted by the yielding characteristics of the conductive spring I28--I3I until the central contact 21 is in operative position when the leaf spring contacts H9 and I23 have reached the point where they can snap outwardly, due to their inherent resiliency, over the ends of and in electrical contact with the contact prongs I|-I9. The parts are then in position to function as a screw-in plug for electrical connection with a screw socket or other similar device.

The parts are thus fixedly retained in this position. Relative rotation of the threaded shell with respect to the prongs is prevented and the structure is sufliciently rigid and any loose-play prevented by the spring action of the several parts, so that there. is no tendency for the parts to wobble or to collapse into the interior of the body.

To restore the parts to the original position of Figure 3, it is merely necessary to press the insulatory members I II toward one another by a pinching action of the thumb and forefinger. Should the prongs be connected with a source of electrical current at that time, the fingers are nevertheless insulated from the conductive strips by the enclosing insulation III. Collapsing the contact strips as described throws the central contact out of circuit and downward pressure thereon willforce the central contact carrying member downwardly within the shell carrying member 2|. Of course, the shell is similarly out of circuit and can be safely handled also. Continued pressure on the central contact member 25 forces both members downwardly into the interior of the body member I5 where they are retained and latched in position as before.

Various modifications will occur to those skilled in the art in the composition, configuration and disposition of the component elements going to make up the invention as a whole as well as in the selection of features for use in other combinations and no limitation is intended by the phraseology of the foregoing description or illLstrations in the accompanying drawings, except as indicated in the appended claims.

What is claimed is:

1. A dual purpose contact plug comprising a cup-shaped body member, spaced contact prongs carried therewithin and extending therewithout, a threaded shell carrying member formed with a bore and reciprocable into and out of the body, a threaded shell carried by said last named member for electrical engagement with the threaded contact in a socket, a central contact member reciprocable into and out of the bore in the shell carrying member from a protracted position without the bore to a retracted position within the bore and a central contact carried by said contact member for electrical contact with a central contact in a socket in protracted position.

2. A dual purpose contact plug comprising a cup-shaped body'member, spaced contact prongs carried therewithin and extending therewithout, a threaded shell carrying member formed with a bore and reciprocable into and out of the body, a threaded shell carried by said last named memher for electrical engagement with the threaded contact in a socket, a central contact-member reciprocable Intoand out of the bore in the shell carrying member from a protracted position without the bore to a retracted position within the bore, a central contact carried by said contact member for electrical contact with a central contact in a socket in protracted position and means i norm-ally retracting the central contact member into the bore.

3. A dual purpose contact plug comprising a cup-shaped body member, spaced contact prongs carried therewithin and extending therewithout, a threaded shel-l carrying member formed with a bore and reciprocable into the body to expose the prongs for insertion in a receptacle and out of the body to conceal and render impossible the insertion of the prongs in a receptacle, a threaded shell carried by said last named member for electrical engagement with the threaded contact in a socket, a central contact carrying member reciprocable into and out the bore in the shell carrying member from a protracted position without the bore to a retracted position within the bore, a central contact carried by said contact member for electricalcontact with a central contact in a socket in protracted position, means to preventseparation of the threaded shell carrying member and the body member comprising a recess in a contact prong and a coacting, extensible stop carried with the central contact carrying member and operative connections preventing separation of the shell carrying member and the central contact carrying member.

4. In a dual purpose electrical contact plug, in combination, a hollow cup-shaped body member, two spaced substantially parallel conductive contact prongs secured in the body member and extending therewithout, a tubular intermediate member oi a cross-sectional area to enter the body member and formed to receive the prongs,

a threaded shel-l carried by the intermediate 3 member, an end member of a cross-sectional area to be received in the intermediate member, a central contact carried by the end member, a movable conductive member carried by the end member and electricallyconnected with the shell and adapted to overlie a prong and make electrical contact therewith in protracted position of the end member.

5. In a dual purpose electrical contact plug, in combination, a hollow cup-shaped body member, two spaced substantially parallel conductive contact prongs secured in the body member and extending therewithout, a tubular intermediate member of a cross-sectional area to enter the body-member and receiving the prongs, a threaded shell carried by said intermediate member, an end member or a cross-sectional area to enter the intermediate member, a central contact carried by the end member and a movable conductive member carried by the end member and electrically connected with the central contact and adapted to overlie the end of a prong in pro-' tracted position of the parts to complete thecir- 1 ,cuit with a prong.

a conductive resilient member electrically con-- nected witheach contact and adapted to overlie the end oi! a prong in protracted position of the end member to retain the members in protracted position.

7. In a dual purpose electrical contact plug, in combination, a hollow cup-shaped body member, two spaced substantially parallel conductive contending therewithout, a tubular intermediate member of a cross-sectional area to enter the body member and receiving the prongs, a threaded shell contact carried by said intermediate member, an end member of a cross-sectional area to enter the intermediate member, a central contact carried by the end member and a conductive resilient member-electrically connected with one of said contacts and carried by the end member and adapted to overlie the end 01' a prong in protracted position of the parts, said central contact carrying member being formed with a recess to receive the conductive resilient member in retracted position 01' the parts,and dielectric material carried by said conductive resilient member to insulate said memberirom 2. prong in retracted position. v

8. In a dual purpose electrical contact plug, in combination, a hollow cup-shaped body member, two spaced substantially parallel conductive contact prongs secured in the body member and extending therewithout, a tubular intermediate member of a cross-sectional area' to enter the body member andreceiving the prongs, athreaded shell contact carried by said intermediate member, an end member of a cross-sectional area to enter the intermediate member, a central contact carried by the end member and a yielding conductive member electrically connected with each contact and adapted to overlie the end of a respective prong in protracted position of the parts and insulating means carried by each resilient member.

9. A dual purpose contact plug comprising a cup-shaped body member oi? insulatory material, spacedlcontact prongs carried therewithin and extending therewithout, a, member carrying 'a conductive threaded shell and formed with a bore and reciprocable into and out of the body, a central contact carrying member reciprocable into and out or the bore in the shell carrying member, resilient conductive retracting means tending .tonormaliy retract the central contact member into the bore in the threaded shell member, said resilient means being in electrical connection with the threaded shell and resilient conductive means in electrical connection with said resilient retracting means and adapted to make electrical connection with a contact prong.

10. A dual purpose contact plug comprising aretracting means and adapted to make electrical tact prongs secured in the body member and exconnection with a contact p'rong, said last named resilient conductive means normally preventing retraction oi the central contact carrying member into the bore in the threaded shell carrying member.

11. In a dual purpose electrical contact plug, in combination, a hollow cup-shaped body member, two spaced substantially parallel conductive contact prongs secured'in the body member and extending therewithout, a tubular intermediate member of a cross-sectional area to enter the body member and receiving the prongs, a threaded shell carried by said intermediate member, an end member of a cross-sectional area to enter the intermediate member, a central contact carried by the end member and a yielding latch member carried by the end member and adapted to overlie the end of a prong in protracted position of the parts to retain the end member in protracted position.

12. In a dual purpose electrical contact plug, in combination, a hollow cup-shaped body member, two spaced substantially parallel conductive contact prongs secured in the body member and extending therewithout, a tubular intermediate member of a cross-sectional area to enter the body member and receiving the prongs, a contact carried by said intermediate member, an end member of a cross-sectional area to enter the intermediate member, a contact carried by the end member and a movable conductive member carried by the end member and electrically connected with one of said contacts and adapted to overlie the end of a prong in protracted position of the parts to complete the circuit with 9. prong.

13. In a dual purpose electrical contact plug, in combinatioma hollow cup-shaped body member, two spaced substantially parallel conductive contact prongs secured in the body member and extending therewithout, a tubular intermediate member of a cross-sectional area to enter the body member and formed to receive the prongs, a threaded shell carried by the intermediate member, an end member of a cross-sectional area to be received in the tubular member, a central contact carried by the end member, a conductive tension member between the intermediate member and the end member and in electrical connection :with the shell and having a portion adapted to overlie a prong and make electrical contact therewith in protracted position of the end and intermediate members.

14. In a dual purpose electrical contact plug, in combination, a hollow cup-shaped body member, two spaced substantially parallel conductive contact prongs secured in the body member and extending therewith, a tubular intermediate member of a cross-sectional area to enter the body member and receiving the prongs, a threaded shell carried by said tubular member, an end member of a cross-sectional area to enter the intermediate member, a central contact carried by the end member, yielding conductive latch members carried by the end member and adapted to respectively overlie the prongs in protracted position of the parts, a conductive connection between the central contact and a latch member and a conductive expansible connection between the threaded shell and the other latch member urging the end member to retracted position.

15. In a dual purpose electrical contact plug, in combination, a hollow cup-shaped body member, two spaced substantially parallel conductive contact prongs secured in the body member, a tubular threaded shell carrying member of a crosssectional area to enter the body member and receiving the prongs, a threaded shell carried by said cylindrical member, a central contact carrying member of a cross-sectional area to enter the shell carrying member, a stop carried by the shell carrying member, a stop carried by a prong engaged by the first named stop in protracted position of the parts to limit out-ward movement thereof and a conductive resilient member carried by the central contact member and adapted to overlie the end of a prong in protracted position of the parts.

DONALD E. WADSWORTH. 

